1. Field of the Invention
The present invention relates to a wireless (radio) ATM (Asynchronous Transfer Mode) communication system, and more particularly, to a wireless ATM communication system capable of improving a transmission efficiency of a radio section in which the TDMA (Time Division Multiple Access) transmission system is employed.
2. Description of the Related Art
As to wireless ATM communication systems employing the TDMA transmission system in the radio section, the following communication systems have been proposed.
Japanese Patent Application Laid-open No. Hei 9-83518 discloses the method for effectively transmitting ATM cells by a form of the TDMA data burst in the TDMA transmission system between a terrestrial communication network and a satellite communication network with suppressing deterioration of transmission quality caused by the CDV (Cell Delay Variation).
Japanese Patent Application Laid-open No. Hei 9-18435 discloses the system which improves a transmission efficiency in a radio section of a wireless ATM communication system by allocating a single burst as to the down link transmission (namely, direction from a base station to a terminal station), and allocating dynamically the bursts based upon the ALOHA access control theory as to the up link transmission (namely, direction from a terminal station to a base station) in the TDMA transmission system.
Japanese Patent Application Laid-open No. Hei 7-336774 discloses the TDMA mobile telephone system which is flexible for allocating the time slots reserved for the packet data transmission and capable of varying the number of the time slots of the TDMA frame as required.
In the conventional wireless ATM communication system employing the TDMA transmission system in the radio section, in which slots or bursts on TDMA frame of the user channels usable for the respective users are pre-determined through the control channels, and burst data of xe2x80x9ckxe2x80x9d pieces of ATM cells is transmitted and received via this user channel, xe2x80x9cnxe2x80x9d (nxe2x89xa71) of user channels are fixedly assigned when the connection is established. As a consequence, when no data is transmitted, or when not all of the assigned bursts are utilized for data transmission due to throughput of data to be transmitted is less than maximum throughput usable in reserved user channel, not all the assigned user channels are used for data transmission and causing deterioration of usage efficiency of transmission resources.
The present invention has been made to solve the above-mentioned conventional problems, and therefore, has an object to provide a wireless ATM communication system capable of improving a transmission efficiency of a radio section in which the TDMA transmission system is employed.
An idle portion of user data channel allocated to a certain user can be used when excess ATM cells are to be transmitted by other user. The slot position information of user data channel of other user, which can be used for excess ATM cells transfer of own data, is contained in the control channel and notified to the terminal station. The terminal station extracts data in the slot position of user data channel of other user indicated by the control channel in addition to data extract from own user data channel allocated at the time of connection establishment.
To achieve the above-described object, a wireless ATM communication system, according to an aspect of the present invention, is featured by such a wireless ATM communication system transmitting and receiving data of ATM cells by a radio system employing the TDMA system comprises a base station for assigning a data channel for a user who has requested connection establishment, for assigning a part of user channel being assigned to other user but not used all part of the user channel as an additional user channel when amount of data to be transmitted from the base station being detected to be too large to carry by the assigned user channel, and for transmitting a control channel in which slot positions of the additional user channel is indicated; and a terminal station for detecting use of additional user channel indicated in the control channel, and for receiving the data in designated slot positions of the additional user channel in addition to the data in the user channel assigned for own station.
The base station according to the present invention comprises data management means for detecting amount of data to be transmitted for each terminal station when commencing data communication with one of terminal stations, for allocating additional user channel, which has allocated to other terminal station but containing available portion not used, to the terminal station when an allocated user channel to the terminal station.: being not enough to carry amount of data to be transmitted to the terminal station, and for outputting user channel allocation information; and data assembling means for assembling slot position information of the additional user channel in a control channel, for assembling ATM cells to be transmitted to the terminal station in the allocated user channel and designated portion of the additional user channel, and for producing a TDMA frame including the control channels and user data channels to be transmitted to the terminal stations.
The terminal station according to the present invention comprises receive signal de-assembling means for de-assembling a TDMA frame transmitted from the base station into control channels and user channels, and for discriminating channels for own terminal station; receive slot allocation information producing means for extracting slot positional information of the allocated user channel and the additional user channel indicated in the control channel output from the receive signal de-assembling means; receive slot timing producing means for providing timing signal to the receive signal de-assembling means for extracting user data from user channels; ATM cell extracting process means for extracting ATM cells from the user data extracted from the receive signal de-assembling means; and ATM cell processing means for filtering ATM cells directed to own terminal station among ATM cells extracted by the ATM cell extracting process means based upon header information of each ATM cell, and for processing the filtered ATM cells as received data.